Thiophene separation from n-paraffin compounds using three Methylimidazolium Hexafluorophosphate base ionic solvents

This study presents an experimental investigation into the desulfurization of model diesel fuels via liquid–liquid extraction of thiophene (C₄H₄S) from aliphatic hydrocarbons using imidazolium-based ionic liquids as selective solvents. The ionic liquids evaluated are 1-pentyl-3-methylimidazolium hexafluorophosphate [C ₅ mim][PF₆], 1-hexyl-3-methylimidazolium hexafluorophosphate [C ₆ mim][PF₆], and 1-heptyl-3-methylimidazolium hexafluorophosphate [C ₇ mim][PF₆]. Liquid–liquid equilibrium (LLE) data were obtained at 313.15 K and atmospheric pressure (101.3 kPa) for nine ternary systems comprising n-dodecane, n-tetradecane, or n-hexadecane with thiophene and one of the selected ionic liquids. Distribution ratios and selectivity values were determined and compared across the investigated systems to evaluate the desulfurization efficiency. The influence of alkyl chain length in both the hydrocarbon and ionic liquid phases was examined. Experimental data were correlated using the Non-Random Two-Liquid (NRTL) activity coefficient model, with binary interaction parameters reported. The model accurately represented the experimental phase behavior, achieving an average root-mean-square deviation (RMSD) of 0.1355. Ternary phase diagrams, incorporating both experimental measurements and calculated tie-lines, were constructed to evaluate extraction performance. The results confirm the superior efficiency of thiophene removal ( K  = 3.03–4.87, S  = 548–946) using [C₅mim][PF₆], [C₆mim][PF₆], and [C₇mim][PF₆], compared to literature values reported for fuel purification processes.